The term "magnetic susceptibility" as used herein means the combined properties of a material which render it more or less easily magnetized, including its permeability, retentivity, coercivity, and so on. Ferromagnetic materials such as mild steel exhibit relatively high magnetic susceptibility, especially when alloyed with silicon or aluminum. Stainless steels, on the other hand, are typically of low magnetic susceptibility.
Ultrasonic pipe weld inspection is carried out, particularly in nuclear power plants, by a weld scanner device which is self-driven around the circumference of the pipe at the chosen weld and is held magnetically in place against the pipe surface regardless of the orientation of the pipe to ground. Scanners typically include a cylindrical wheel which rolls about the pipe and which has a circumferential groove of rectangular cross section. The grooved wheel rides on a flexible guide which is belted securely about the pipe. When the pipe is of stainless steel, which is often the case in nuclear power plants, a magnetically susceptible track must be associated with the flexible guide so that the scanner can hold itself magnetically in place relative to the pipe surface as it rolls around the pipe during the inspection process.
Prior art scanner tracks have been of magnetically susceptible sheet metal with nylon belts and buckles at the opposite ends thereof for attachment to a pipe. They do not permit the scanner to complete a full 360.degree. examination of the pipe weld without repositioning the belted track at least once. Attachment of prior art belted tracks is difficult and, including repositioning time, often takes longer than the examination itself. Also the belts, buckles and associated attachment pins are essentially loose parts which could inadvertently be lost during use. Tensioning buckles used in prior art tracks are of the ratchet type adjustable only in coarse increments so that considerable force is often required to secure the assembly to the pipe. Another disadvantage has been that if the scanner reaches stops at the track ends it can fall off, and hence safety cables are necessary connecting the scanner to the track. These safety cables occasionally become entangled in the magnetic wheels of the scanner.